Which one should i watch Fullmetal Alchemist or Full Metal Alchemist: Brother hood?

I think you should watch both of them and that you should start with Full Metal Alchemist.
And then go on to Full Metal Alchemist: Brotherhood
I`m actully doing that right now or i start a while atrás so now i`m close to the last episode in brotherhood xD
Well this is my opinion :) Do what you want ;)

first watch fma then fma:brotherhood it will make a lot mais sense 2 u trust me

u should watch both it doesn't matter i think there both good but i started on full metal alchemist and its better 2 start on

IMO, i dont like brotherhood at all, if you watch brotherhood, and not the first one, then you miss out on the first intended moral of the show. but, if you watch the original, it makes much mais sense (to me) and is very awesome! XD

You should watch both.
Most people watch the FMA first then the FMAB because that's the order they came in.
FMA has a better begining and tells the details of that and follows that manga. While FMAB, since people have already seen the begining the right way, kinda skips over it or adds stuff or leaves stuff out. But then FMA has a really crappy ending. Oh well I think you should watch FMA first and then FMAB.
Kinda like eating veggies then sugar :)
But when you're done watching FMA be sure to watch the movie next.